Thursday afternoon five -- -- PM. Amid a flurry of rumors and growing impatience the FBI finally shows -- -- Today we are listing the public's help to identify the two suspects -- now -- images they are identified -- suspects one. And suspects who they appear to be associated. For the first time the world sees the faces of evil yeah. Hope is that the public will help the FBI -- -- mountain. Somebody out there knows these individuals as friends and neighbors coworkers. Or family members of the suspects we've never seen anything quite like this yeah where they're actually asking people just look out for somebody. But to turn in their cameras. Minutes later the FBI web site crashes so many clicks. Tips make their way in fast and furious among them David -- says he has a picture that may help. The FBI releases that shot a clear image of suspects to. Turns out many people not only recognized -- cars -- 9 AM but quite a few when his classmates against the hadn't called authorities because they couldn't believe the guy they knew -- been a bomber. Is actually -- very nice didn't get along with them very well I can't say -- enough he's just not the guys. He's just not -- do it and didn't expect anything like this from him. -- -- nine grows late -- Bostonians go to bed still no word if any actionable leads to comment. Later that night this silence is broken. Shots are fired 26 year old MIT police officers Sean collier is fatally wounded and an MIT police officer. -- was shot and killed in the line of duty tonight and suddenly the campus this morning police and news crews from Disney connected to the bombings in these moments later not far away a man driving the black Mercedes suvs says he's attempted gunpoint by two men. He later tells police the -- reveal themselves as the bombers and dropped him unharmed at a gas station. Police are in pursuit of the Mercedes and a high speed chase through residential neighborhoods. There are about half a dozen police cars that immediately got up and took off in the other direction it is an incredibly fluid situation. -- -- Tossing grenades from this whole floor -- heavy winds. The end up about five miles away in the small community of Watertown. One half time. -- -- about forty to 45 police officers coming down their cars so I got on the balcony to see when -- could see at which point I heard a very very loud explosion and boom. I didn't see it but as I looked up in the sky could see -- lit up the entire sky -- on Watertown. In the melee a transit cop is seriously injured. Suspect number 110 Marlins and -- -- runs toward police. Minutes later while escaping police in the stolen vehicle -- -- -- runs over his own brother who later dies. -- car eventually police on. Police and federal authorities greater. -- your voice territory armed and dangerous suspects. Around two million police begin a -- -- every person in town with a warning. Stay inside don't open your doors here. Remain indoors until further notice. At a local -- This. -- does not supposed to happen here. For an entire day close to a million people are ordered not to leave their homes. By evening the lockdown is finally lifted. 9 PM news that the suspect is in custody. -- the investigation is far. From over though the FBI has an enormous task ahead of even the once it catches -- garden. Because they have to find all of his known friends all of -- little disclosures. The same -- his brother this case will be an open case for weeks if not months in the future.

This transcript has been automatically generated and may not be 100% accurate.

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